KR100898946B1 - Ultrasound Diagnostic System and Method for Elastic Image Formation - Google Patents

Abstract

The present invention provides an ultrasound diagnosis system and method for accurately forming a correlation between received signals when stress is applied and when stress is not applied, and forming an elastic image under objective conditions. To this end, when the stress is not applied to the object, a first transmission pulse is formed, and when the stress is applied, a second transmission pulse having a waveform different from the first transmission pulse is formed, and the first transmission pulse and the second transmission pulse are respectively formed. Corresponding first and second received signals are formed, a strain of the object is calculated based on the first and second received signals, the compression rate is estimated, and an elastic image is formed based on the first and second received signals.

Ultrasonic wave, elasticity, strain, transmission pulse, compression rate

Description

ULTRASOUND DIAGNOSTIC SYSTEM FOR FORMING ELASTIC IMAGE AND METHOD}

1 is a graph showing the change in the length of the received signal according to the presence or absence of stress.

Figure 2 is a block diagram showing the configuration of an ultrasound diagnostic system according to a first embodiment of the present invention.

3 is a block diagram showing the configuration of a probe provided in the ultrasonic diagnostic system shown in FIG.

Figure 4 is a block diagram showing the configuration of an ultrasound diagnostic system according to a second embodiment of the present invention.

The present invention relates to an ultrasound diagnostic system and method, and more particularly to an ultrasound diagnostic system and method for forming an elastic image.

The ultrasound diagnosis system transmits an ultrasound signal to the object, receives an ultrasound echo signal reflected from the surface of the reflector in the object, converts the ultrasound echo signal into an electrical reception signal, and outputs the image through a predetermined image processing, thereby causing an internal state of the object. Diagnose

Among various methods of diagnosing diseases based on ultrasound images, there is an elastic imaging method that analyzes lesions in a human body by using a difference in mechanical response of a medium when external force, that is, stress is applied or not. Elastic imaging uses the elasticity of tissues associated with pathological phenomena. For example, abnormal tissues, such as cancer and tumors, are harder than normal tissues, and thus, when externally stressed the same size, they are less deformed than soft normal tissues. In particular, in B-mode (brightness-mode) imaging, it is difficult to distinguish the scattering efficiency between the normal tissue and the abnormal tissue because the scattering efficiency is not large.

The elastic imaging method may be classified into an elastic modulus imaging method for imaging an elastic modulus of a tissue and a strain imaging method considering strain, that is, a strain of a medium against stress. The relative position of the reflector in the object is determined from the movement of the received signal due to stress, and the elastic modulus or strain (strain) profile of the tissue is reconstructed in one, two, or three dimensions to determine the location, size, It can diagnose the condition.

Looking at the deformation of the one-dimensional medium, the relationship between stress σ, elastic modulus E, strain ε is established as shown in the following equation (1).

The elastic modulus imaging method obtains a profile of the elastic modulus E based on Equation 1, and the strain imaging method obtains a profile of the strain ε. The elastic modulus imaging method, which requires stress estimation to obtain the elastic modulus, is a quantitative method, and the strain imaging method is a qualitative method because the stress is approximated as a constant. Since the elastic modulus imaging method is difficult to use because it has a limitation to solve the inverse problem, many studies on the strain imaging method have been conducted since the early 1990s.

In order to obtain the elasticity information of the tissue, that is, the elastic modulus or strain, the first received signal when no stress is applied and the second received signal when stress is applied are compared. Since the first received signal is a reflected ultrasound signal from an uncompressed object and the second received signal is a reflected ultrasound signal from a compressed object, as shown in FIG. 1, the second received signal is a compressed form of the first received signal. Becomes In order to compare the first received signal with the second received signal, the size of the object, more specifically, the distance between the reflectors in the object must be restored to the same condition, thereby extending the second received signal. However, since the prior art transmits pulses of the same waveform into the human body when it is not stressed or when it is applied, when the second reception signal is extended, the spacing between the reflectors is restored to its original state, but the width of the transmission pulse is also increased, which adversely affects strain estimation. A problem arises that degrades the correlation between the first received signal and the second received signal.

Hereinafter, the problems of the prior art will be described in more detail.

라 하고, 반사체의 위치를 나타내는 산란 함수를

라 하면, 수신신호

는 다음의 수학식 2와 같이 표현할 수 있다.Transmit pulse signal to obtain B-mode ultrasound image

Scatter function representing the position of the reflector

In other words, the received signal

Can be expressed as Equation 2 below.

'*' In Equation 2 represents a convolution.

When the reflection coefficient of the reflector is A, the distance between the transducer and the reflector d, the sound velocity is C, and the total number of reflectors in the object is N, the scattering function is given by Equation 3 below.

를 이용하였을 때, 스트레스를 가하지 않을 경우의 제1 수신신호

와 스트레스를 가할 경우의 제2 수신신호

는 다음의 수학식 4와 같이 주어진다. 수학식 4와 5에서

와

는 각각 스트레스를 가하지 않을 경우와 스트레스를 가할 경우의 산란함수를 나타낸다.Same transmission pulse

When using, the first received signal when no stress

Received signal in case of stress and stress

Is given by Equation 4 below. In Equations 4 and 5

Wow

Are scattering functions when stress is not applied and stress is applied, respectively.

(

)라 할 때, 수학식 4와 수학식 5로부터 스트레스 유무에 따른 산란 함수는 다음의 수학식 6과 같은 관계를 갖는다.The compression rate of the second received signal

(

), The scattering function according to the presence or absence of stress from the equations (4) and (5) has the same relationship as the following equation (6).

It can be seen from Equation 6 that the spacing between the reflectors narrows as the stress is applied.

와 제2 수신신호

를 비교하여 변형률을 구하기 위해, 초음파 영상의 깊이방향으로 두 수신신호

와

를 다수의 세그먼트(segment)로 나누고, 두 수신신호의 대응 세그먼트 간의 상관함수(cross correlation)를 취하고, 상관함수가 최대가 되는 지연 시간을 계산하고 미분을 구하면 변형률을 추정해낼 수 있다.First reception signal

And a second received signal

In order to find the strain by comparing the two signals in the depth direction of the ultrasound image

Wow

It is possible to estimate the strain by dividing into a plurality of segments, taking a cross correlation between corresponding segments of two received signals, calculating a delay time when the correlation function is maximized, and obtaining a derivative.

The following equation (7) is obtained from equations (5) and (6), and is expanded in the time domain to obtain equation (8).

를 시간축으로 신장시키면 송신펄스

도 신장된다. 따라서, 스트레스 유무에 관계없이 동일한 송신펄스

를 인가하였음에도 불구하고, 수학식 8에서와 같이

에는 신장된 송신펄스가

가 반영되어 제1 수신신호

와 제2 수신신호

를 시간축으로 신장시킨

의 상관함수의 최대치를 정확하게 얻기가 어렵다. 특히, 인체 내의 반사체의 밀도는 단위 파장 당 수십 개 정도에 달하므로 제1 수신신호

와 제2 수신신호

의 파형이 많이 달라져 두 신호 사이의 상관도를 파악하기가 더욱 어려워지는 문제점이 있다.As can be seen from Equation 8, the second received signal

Transmit pulse on time axis

Is also elongated. Therefore, the same transmission pulse with or without stress

In spite of the

There is an extended transmission pulse

Is reflected to the first received signal

And a second received signal

Is elongated to the time base

It is difficult to accurately obtain the maximum value of In particular, since the density of the reflector in the human body reaches about tens per unit wavelength, the first received signal

And a second received signal

Since the waveforms of the signals vary greatly, it becomes more difficult to determine the correlation between the two signals.

The present invention for solving the above-described problems, it is possible to more accurately obtain the correlation between the received signal when the stress is applied and not, and to provide an ultrasonic diagnostic system and method for forming an elastic image under more objective conditions The purpose is.

Ultrasonic diagnostic system according to the present invention, a transmission pulse forming unit for forming a first transmission pulse when the stress is not applied to the object, and a second transmission pulse having a waveform different from the first transmission pulse when the stress is applied; Converting the first transmission pulse or the second transmission pulse into an ultrasound signal and transmitting the ultrasound signal to the object, and corresponding to the first transmission pulse and the second transmission pulse based on ultrasound echo signals input from the object; A probe forming a first received signal and a second received signal; A frame data forming unit configured to form first frame data and second frame data based on the first and second received signals, respectively; A storage unit which stores the frame data in frame order; A processor configured to calculate a displacement of the object and a strain of the object based on the stress based on the first and second received signals, and estimate a compression rate based on the displacement; A post processor configured to form an elastic image based on the compression rate and the strain rate; And a display unit displaying the elastic image.

 Ultrasonic diagnostic system according to the present invention, the transmission pulse forming unit for forming a first transmission pulse when the stress is not applied to the object, and a second transmission pulse having a waveform different from the first transmission pulse when the stress is applied; The first transmission pulse or the second transmission pulse is converted into an ultrasonic signal and transmitted to an object, and a first reception corresponding to the first transmission pulse and the second transmission pulse, respectively, based on ultrasonic echo signals input from the object. A probe forming a signal and a second received signal; A frame data forming unit configured to form first frame data and second frame data based on the first and second received signals, respectively; A storage unit which stores the frame data in frame order; A preprocessing unit extracting the second frame data and the second frame data to log-compress the first and second received signals focused on each frame data; A processor that calculates a displacement based on the log-compressed first and second received signals, calculates a strain by differentiating the displacement with respect to a distance, and estimates a compression rate based on the displacement; A post processor configured to form an elastic image based on the compression rate and the strain rate; And a display unit displaying the elastic image.

In the elastic image forming method according to the present invention, when the stress is not applied to the object to form a first transmission pulse, when the stress is applied to form a second transmission pulse having a waveform different from the first transmission pulse, Transmitting a transmission pulse or a second transmission pulse to an ultrasonic signal and transmitting the same to an object, and forming a reception signal based on ultrasonic echo signals input from the object, respectively, in the first transmission pulse and the second transmission pulse. Correspondingly, a first received signal and a second received signal are formed, and the received signal is focused to form frame data. The first and second received signals are focused, respectively, to thereby first and second frame data. And store the frame data in frame order, and calculate the displacement and strain of the object based on the first and second received signals. Output, and estimating a compressibility based on the displacement, and on the basis of the compression ratio and the strain comprises forming an elastic image.

Hereinafter, an ultrasound diagnosis system and an elastic imaging method according to the present invention will be described with reference to the accompanying drawings.

As shown in FIG. 2, the ultrasound diagnosis system 100 according to the present invention includes a transmission pulse forming unit 10, a probe 20, a frame data forming unit 30, a storage unit 40, and a preprocessing unit (pre). a processing unit 50, a processor 60, a post-processing unit 70, and a display unit 80. In addition, the ultrasound diagnosis system 100 further includes a user input unit 101 and a stress detector 102.

The transmission pulse forming unit 10 forms a first transmission pulse when no stress is applied to the object, and forms a second transmission pulse having a waveform different from the first transmission pulse when the stress is applied. The first transmission pulse and the second transmission pulse are transmission pulses for forming a B-mode ultrasound image. The object includes all of the reflector in the object, the medium around the reflector, and the like.

The probe 20 converts the first transmission pulse or the second transmission pulse into a first ultrasound transmission signal and a second ultrasound transmission signal, respectively, and transmits the same to the object, and forms a received signal based on the ultrasound echo signal input from the object. . The probe 20 forms a first reception signal and a second reception signal in correspondence with the first transmission pulse and the second transmission pulse, respectively.

The frame data forming unit 30 focuses the first received signal or the second received signal to form frame data. Frame data may be in the form of RF data or baseband complex data.

The storage unit 40 stores frame data in frame order. The storage unit 40 stores first frame data formed by concentrating the first received signal and second frame data formed by converging the second received signal.

The preprocessing unit 50 extracts the first and second frame data from the storage unit 40 to log-compress the first received signal and the second received signal to increase the amplitude, and an error due to noise. Decreases. Log compression is a technique well known in the art to which the present invention pertains, and a detailed method thereof is omitted.

)로 추정한다. 인체와 같이 구성이 복잡한 대상체 내부의 경우 탄성 계수가 일정하지 않으므로, 주사선 마다 압축률(

)이 달라지므로, 이를 고려하여, 프로세서(60)는 모든 주사선에 대해 압축률(

)을 계산한 뒤 평균 압축률(

)을 산출한다. 압축률은 스트레스에 비례하므로, 산출된 평균 압축률을 평균 스트레스로 간주할 수 있다. 후처리부(70)는 다음의 수학식 9와 같이 변형률을 평균 압축률(

)로 나누어 정규화된 탄성영상을 형성하고, 변형률을 크기에 따라 슈도우 칼라(pseudo color)로 맵핑한다.The processor 60 calculates the strain of the object from the preprocessed frame data and estimates the compression rate. In more detail, the processor 60 may perform the displacement by a cross-correlation method or an auto-correlation method based on the first and second received signals with and without stress. The displacement is differentiated with respect to the distance to yield local displacement, ie strain (strain). Since the strain calculation method is well known in the art to which the present invention pertains, a detailed description thereof will be omitted. In addition, the processor 60 may determine the maximum value of the displacements calculated using the autocorrelation or cross-correlation of the first and second received signals.

Estimate). Since the elastic modulus is not constant in a complex object such as a human body, the compression rate (for each scan line)

), The processor 60 may compress the compression rate (i.e.,

), Then the average compression rate (

) Is calculated. Since the compressibility is proportional to the stress, the calculated average compressibility can be regarded as the average stress. The post-processing unit 70 calculates the strain rate as the average compression rate (9).

Normalized elastic images are formed by dividing by), and the strains are mapped to pseudo colors according to the size.

The contrast of the elastic image varies depending on the magnitude of the stress applied, and the magnitude of the stress varies depending on the speed applied, the user's skill level, and the like. In addition, the post processor 70 obtains a normalized strain, and then performs low pass filtering or median filtering to reduce noise.

The display unit 80 displays the B-mode ultrasound image based on the frame data input from the frame data forming unit 30, and displays the elastic image input from the post processing unit 70. The display 80 may display the elastic image together with the B-mode image.

The user input unit 101 receives a stress start signal from which the stress starts to be applied to the object.

The stress detector 102 detects that stress is applied to the object through the probe 20 and generates a stress detection signal. The stress detector 102 may be attached to the probe 20 as shown in FIG. 3. The probe 20 of the ultrasound diagnostic system according to the present invention may include a stress transmitter 21 surrounding a scan surface, and the stress detector 102 may be mounted on the stress transmitter 21. As described above, the probe 20 having the stress transmitter 21 may be used to apply stress to the object more uniformly.

Hereinafter, a method of forming the first transmission pulse and the second transmission pulse having different waveforms in the transmission pulse forming unit 10 will be described in more detail.

) 또는 평균 압 축률(

)을 반영하여 형성한다. 즉, 스트레스를 가하지 않을 때는 압축률이 적용되지 않은 제1 송신펄스

를 생성하고, 스트레스를 가할 때는 프로세서(60)로부터 입력되는 압축률을 적용하여 제1 송신펄스

의 파형을 시간 축에서 압축한 제2 송신펄스

를 생성한다. 제1 송신펄스

와 제2 송신펄스

는 다음의 수학식 10과 같은 관계를 갖는다.The transmission pulse forming unit 10 forms a second transmission pulse in response to the stress start signal input from the user input unit 101 or the stress detection signal from the stress detection unit 102. The second transmit pulse is the compression rate (input) input from the processor 60

) Or average compression rate (

To reflect). That is, when no stress is applied, the first transmission pulse to which the compression rate is not applied

To generate a first transmission pulse by applying a compression rate input from the processor 60 when applying stress

Transmission pulses in which the waveform of the waveform is compressed on the time axis

Create 1st transmission pulse

And second transmission pulse

Has a relationship as shown in Equation 10 below.

와

는 다음의 수학식 11과 12와 같이 표현된다.Received signals corresponding to non-stressed transmission pulses, i.e., transmission pulses without compression rate and transmission pulses with compression rate, respectively

Wow

Is represented by the following Equations 11 and 12.

는 다음의 수학식 13과 같이 표현된다.As described above, when the transmission pulse is compressed on the time axis to reflect the compression rate of the object due to stress, the received signal

Is expressed by Equation 13 below.

를 시간축 상에서 압축률(

) 만큼 신장시켜주면 수신신호

같아진다. 매질에 가해지는 스트레스를 고려하여 스트레스가 가해질 때의 송신펄스를 압축률을 적용하여 형성하면, 스트레스를 가할 때 얻어지는 수신신호와 스트레스를 가하지 않을 때 얻어지는 수신신호의 상관도가 높아져 변형률 추정성능이 향상된다. 즉, 수학식 12 및 13으로부터 수신신호

,

는 다음의 수학식 14와 같은 관계를 갖는다.Thus, the received signal

On the time base

If you increase by)

Become the same. By considering the stress applied to the medium and forming the transmission pulses when the stress is applied by applying the compression rate, the correlation between the received signal obtained when the stress is applied and the received signal obtained when the stress is not applied increases and the strain estimation performance is improved. . That is, the received signal from the equations (12) and (13)

,

Has a relationship as shown in Equation 14 below.

를 시간축 상에서

만큼 신장시키면, 스트레스를 가하지 않을 때의 수신신호

와 같아진다. 따라서, 압축률(

)을 알면,

값을 반영하여 변형률을 구할 수 있다.Received signal when stress is applied from Equation (14)

On the time base

When extended by, the received signal when no stress is applied

Becomes the same as Therefore, the compression rate (

),

The strain can be obtained by reflecting the value.

On the other hand, since the extrusion rate within the human body is usually within 10%, the spectrum is widened by compressing the transmission pulses in the same time axis as in the present invention, but the bandwidth of the transducer is not large, and the effect of compression is not large.

Figure 4 is a block diagram showing the configuration of an ultrasound diagnostic system according to a second embodiment of the present invention. The ultrasound diagnosis system 200 further includes a lateral motion estimator 103 in the configuration of the ultrasound diagnosis system shown in FIG. 1.

The lateral motion estimator 103 receives the preprocessed first and second received signals in order, and estimates a change in motion of the object under stress. When stress is applied, the elasticity of the medium in the human body is uneven, so that the movement of the reflector appears in the lateral direction. This lateral movement increases the uncorrelation of the signal and causes calculation errors. Therefore, the lateral motion must be calculated and compensated in the continuous frame data. The lateral motion calculation finds the magnitude of the motion by calculating the pattern matching method of the speckle in the B-mode image or the correlation between adjacent scan lines in two consecutive image data. If lateral motion is observed in two adjacent frame signals, the displacement is calculated for the moving part.

The processor 60 calculates the strain of the object from the preprocessed frame data by reflecting the displacement from the lateral motion estimator 103.

Transmission pulse forming unit 10, probe 20, frame data forming unit 30, storage unit 40, preprocessor 50, processor 60, post processor 70 of ultrasonic diagnostic system 200. Since the configuration of the display unit 80, the user input unit 101, and the stress detector 102 has the same configuration and function as those of the ultrasound diagnosis system 100 of FIG. 1, detailed description thereof will be omitted.

While the present invention has been described and illustrated by way of preferred embodiments, those skilled in the art will recognize that various modifications and changes can be made without departing from the spirit and scope of the appended claims.

The present invention can improve the correlation between the received signal changes depending on the presence or absence of stress by transmitting a transmission signal having a different waveform when the stress is applied and when not.

In addition, by normalizing the elastic image by reflecting the average of the compression ratios that are different for each scan line, it is possible to reduce the influence of the stress magnitude change depending on the subjective tendency of the user.

Claims (22)

delete delete delete A transmission pulse forming unit for forming a first transmission pulse when no stress is applied to the object, and forming a second transmission pulse having a waveform different from the first transmission signal when the stress is applied; Converting the first transmission pulse or the second transmission pulse into an ultrasonic signal and transmitting the ultrasound signal to the object, receiving ultrasonic echo signals reflected from the object, and corresponding to the first transmission pulse and the second transmission pulse, respectively; A probe forming a received signal and a second received signal; A frame data forming unit configured to receive the first received signal and the second received signal to form first frame data and second frame data, respectively; A preprocessor configured to extract the first and second received signals from the second frame data and the second frame data, and log-compress the first and second received signals focused on the respective frame data; Receiving the log-compressed first and second received signals to calculate the displacement of the object according to the stress, calculate the strain of the object by differentiating the displacement with respect to the distance, and calculates the compression rate based on the displacement Estimating processor; A post processor configured to receive the compression rate and the strain to form an elastic image; And Ultrasonic diagnostic system comprising a display unit for displaying the elastic image. The method of claim 4, wherein The transmission pulse forming unit reflects the compression ratio to form the second transmission pulse. The method of claim 4, wherein The ultrasound system Further comprising a side motion estimation unit for estimating the movement of the subject to the stress from the log-compressed first and second received signal, And the processor calculates the strain by reflecting the displacement. The method of claim 5, wherein The probe comprises a plurality of transducers, The processor calculates a compression rate for every scan line from each transducer of the probe to the object, And an average compression ratio is calculated by averaging the compression ratios of all the scan lines. The method of claim 7, wherein And the transmission pulse forming unit forms the second transmission pulse by reflecting the average compression ratio. The method of claim 5, wherein The ultrasound diagnostic system Further comprising a stress detecting unit for generating a stress detection signal by detecting the stress applied to the object, The transmission pulse forming unit And generating the second transmission pulse in response to the stress detection signal. The method of claim 5, wherein The ultrasound diagnostic system Further comprising a user input unit for receiving a stress start signal from the user, The transmission pulse forming unit And generating the second transmission pulse in response to the stress start signal. The method of claim 5, wherein And the post-processing unit forms a normalized elastic image by dividing the strain by the average compression rate. delete delete delete Forming a first transmission pulse when no stress is applied to the object, and forming a second transmission pulse having a waveform different from the first transmission pulse when the stress is applied; Converting the first transmission pulse or the second transmission pulse into an ultrasonic signal and transmitting the ultrasound signal to the object; Receiving ultrasonic echo signals input from the object to form a reception signal, and forming a first reception signal and a second reception signal corresponding to the first transmission pulse and the second transmission pulse, respectively; Concentrating the received signal to form frame data, and condensing the first and second received signals to form first frame data and second frame data; Extracting the first and second received signals from the first frame data and the second frame data, respectively, and log-compressing the first and second received signals focused on the respective frame data; Calculating the displacement of the object according to the stress by receiving the log-compressed first and second received signals, differentiating the displacement with respect to a distance, and calculating a strain rate; Estimating a compression rate by receiving the displacement; And And forming an elastic image by receiving the compression rate and the strain rate. The method of claim 15, And the second transmission pulse is formed by reflecting the compression ratio. The method of claim 15, Estimating a motion of the object according to stress from the log-compressed first and second received signals; The displacement is calculated by reflecting the movement of the object under the stress. The method of claim 16, The first received signal or the second received signal is obtained through a probe including a plurality of transducers, The compression rate is calculated for every scan line from each transducer of the probe to the subject, And an average compression ratio is calculated by averaging the compression ratios of all the scan lines. The method of claim 18, And the second transmission pulse is formed by reflecting the average compression ratio. The method of claim 16, The method may further include generating a stress detection signal by detecting a stress applied to the object. And generating the second transmission pulse in response to the stress detection signal. The method of claim 17, Further comprising the step of receiving a stress start signal from the user, And generating the second transmission pulse in response to the stress start signal. The method of claim 18, And forming a normalized elastic image by dividing the strain by an absolute value of the average compression ratio.

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